1. Field of the Invention
The invention relates to a pipe pig with at least two running legs placed symmetrically around the longitudinal axis of the pig to travel through a pipe line to perform inspection or preparation tasks.
2. Description of the Prior Art
During assembly or reexamination of power plant pipe lines, examination of welding seams, visual checking and other inspection is necessary. As a rule these pipe lines are not accessible from the outside, so that these operations can be performed only by use of a pig on the inside of the pipe line. Difficulties often occur, e.g., at such places in the pipe lines where weld-in flanges (such as item 3 in FIGS. 1 and 2) are present and the pipe inside surface correspondingly exhibits a hole, or where objects (e.g., temperature measuring sleeves) project into the pipe. Such irregularities of the inside surface of the pipe represent obstacles for the passage of a pipe pig supported on the inside pipe surface on running legs or other runners, since the runners can, for example, fall into such a hole of a weld-in flange and then not permit further travel of the pipe pig.
To reduce this drawback, it is known from DE-OS No. 32 24 498, to provide a pipe pig with three runners disposed about the pig at angles of 120.degree. and to provide each of the runners with two pairs of rollers arranged in tandem. Thus, it is possible, without any problem, to travel over weld-in flanges (e.g., measuring sleeves) whose diameter is clearly less than the diameter of the pipe line being traveled through. However, in the case of larger weld-in flanges, such a pipe pig can no more be used than in the case of a pipe line in which objects project into the inside of the pipe.